Indexing of electronic devices with multiple weight markers

ABSTRACT

A die has a positional location in a wafer defined by first and second coordinates, the first and second coordinates identifying a respective horizontal and vertical location where the die was formed. An index formed on the die has a first comb structure of a first contiguous arrangement of first dots, and a second comb structure of a second contiguous arrangement of second dots. A first marker at a selected one of the first dots indicates a first digit of the first coordinate, and a first additional marker at a selected one of the first dots indicates a second digit of the first coordinate. A second marker at a selected one of the second dots indicates a first digit of the second coordinate, and a second additional marker at a selected one of the second dots indicates a second digit of the second coordinate.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/900,994, filed on Oct. 8, 2010, entitled “Indexing of ElectronicDevices with Multiple Weight Markers,” which claims the priority benefitof Italian patent application number MI2009A001728, filed on Oct. 9,2009, entitled “Indexing of Electronic Devices with Multiple WeightMarkers,” both of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The solution according to one or more embodiments of the presentinvention generally relates to the electronic field. More specifically,this solution relates to the indexing of electronic devices.

Electronic devices are generally integrated in dice, which are formed ina large number of portions of a wafer. Particularly, in a productionprocess of the stepper shot type, each stage of the production processis not performed concurrently on the whole wafer, but step by steprepeating the same operations on different shot areas thereof (by movinga smaller photolithographic mask accordingly).

In this context, it is of the utmost importance to be able to determinethe original position of the dice of the electronic devices in the wafer(before their separation). For example, this information is very usefulfor a quality management of the production process. Indeed, severalcharacteristics of the electronic devices (for example, their functionalparameters, performance and reliability) depend significantly on theposition of the corresponding dice in the wafer (for example, because ofchanges in the crystallographic structure of the wafer through itsextent). Therefore, when some electronic devices are subject to failuresduring their operation and are then returned to a correspondingmanufacturer, the knowledge of their position in the wafer facilitatesthe analysis of the failures and the development of correspondingimprovements in their production process. The same information may alsobe useful during a test of the electronic devices at the wafer level,known as Electrical Wafer Sorting (EWS). Indeed, in this way it ispossible to store the position of any defective electronic devices thatdid not pass the test, so that they may be identified and discardedafter the corresponding dice have been cut (without the need of markingthe dice of the defective electronic devices during the test todiscriminate them—for example, with ink dots).

For this purpose, it is known in the art to form an index on each die(when it is still included in the wafer), which index indicates theposition of the die in the wafer. Particularly, in the case of theproduction process of the stepper shot type, the index has a compositestructure with a shot index (indicating the position of thecorresponding shot area in the wafer) and a die index (indicating theposition of the die in the corresponding shot area). Typically, each(shot and die) index is defined by a row index and a column index, whichdefine a row coordinate and a column coordinate, respectively, in acorresponding matrix. Particularly, a generic index may be implementedwith a ruler (for example, being formed in a surface metallic layer ofthe die), which ruler defines an ordered alignment of locations(referred to as dots) each one associated with a corresponding number; amarker selects a specific dot (for example, by means of the erasure of acorresponding portion of the metallic layer), and then the correspondingnumber. In this case, the die indexes and the rulers of the shot indexesof all the dice may be formed during a selected stage of the productionprocess by means of a corresponding mask (which replicates the samestructures in the different shot areas); the markers of the shot indexesare instead formed by exploiting an additional mask (designed to formthem at the same position in all the corresponding dice), whichadditional mask is however slightly displaced at every shot so as toform these markers at different positions in every shot area. An exampleof the above-mentioned indexing technique is described in United StatesPatent Publication No. 2008/0153250, which is hereby incorporated byreference.

A drawback of the indexing techniques known in the art is theirlimitation in the number of dice that can be indexed in the same wafer.Indeed, the dots of the rulers cannot be smaller than a minimum size(for example, 1 μm×1 μm), in order to allow their correct inspection; inaddition, the area of the dice that can be used to form each ruler isconstrained (for example, with a length of 15 μm). As a result, themaximum value of each row and column index is relatively low (about 15μm/1 μm=15), with a corresponding limitation in the range of each shotand die index (15×15=225 in the example at issue). This drawback isparticularly acute in the die indexes, since the modern productionprocesses easily exceed the above-mentioned number of dice in each shotarea; in this case, it is not possible to implement any indexing of thedice (with a detrimental effect on the quality of the correspondingproduction process).

Different indexing techniques are also known in the art. For example, inJapanese Application 10012527, hereby incorporated by reference, eachindex is represented with a binary code; the bits of the index aredefined in corresponding locations (arranged along a straight line) tothe value 1 in presence of a predefined slit or to the value 0 in itsabsence. The same document also describes other embodiments wherein theindex is represented with a number in a base higher than 2;particularly, the digits of the index are represented by the lengthmultiple of a predefined value of corresponding teeth (in this case,with the index that has a variable length), or by the depth multiple ofa predefined value of slits at the corresponding locations, with thevalue 0 that is represented by the absence of any slit (in this case,with the slits that extend transversally to the arrangement of thelocations).

Alternatively, in Japanese Application 61142734, incorporated byreference, each bit of the index is represented by the length of acorresponding bar (a long bar for the value 0 and a short bar for thevalue 1).

Moreover, in United Stated Patent Application No. 2003/127718,incorporated by reference, each bit of the index is represented at acorresponding location by the presence or the absence of a recess.

SUMMARY OF THE INVENTION

In its general terms, the solution according to one or more embodimentsof is based on the idea of using more markers with different weights(for the definition of a corresponding index).

Particularly, one or more aspects of a solution according to specificembodiments are set out in the independent claims. Advantageous featuresof the same solution are set out in the dependent claims.

More specifically, an aspect of a solution according to an embodimentcomprises an electronic device, which includes a die integrating anelectronic circuit. The die has at least one index; the index includes areference defining an ordered alignment of a plurality of locations onthe die (for example, a ruler with a comb-like structure), and markermeans for defining a value of the index according to an arrangement ofthe marker means with respect to the reference (in other words, thelocations are placed in a straight linear arrangement, wherein a linebest fitting them is straight). In the solution according to anembodiment, the marker means includes a plurality of markers each onearranged at a selected one of the locations; the selected location ofthe marker defines a value of a digit associated with a correspondingpower of a base (higher than 2) within a number in a positional notationin said base, which number represents the value of the index (forexample, in a decimal notation with a marker for the units digit and amarker for the tens digits, each one associated with a correspondingsubset of adjacent locations along the ruler).

A different aspect of a solution according to an embodiment comprises acorresponding indexing method (with the same advantageous featuresrecited in the dependent claims for the electronic device that applymutatis mutandis to the method).

A further aspect of a solution according to an embodiment comprises asoftware program including code means for causing a processing system(for example, a stepper) to perform the steps of this method when thesoftware program is executed on the processing system; a still furtheraspect of the solution according to an embodiment proposes a softwareprogram product including a non-transitory computer readable mediumembodying a software program, the software program including code meansdirectly loadable into a working memory of a processing system therebyconfiguring the processing system to perform the same method.

BRIEF DESCRIPTION OF THE DRAWINGS

A solution according to one or more embodiments, as well as furtherfeatures and the advantages thereof, will be best understood withreference to the following detailed description, given purely by way ofa non-restrictive indication, to be read in conjunction with theaccompanying drawings (wherein corresponding elements are denoted withequal or similar references and their explanation is not repeated forthe sake of brevity, and the name of each entity is generally used todenote both its type and its attributes—such as its value, content andrepresentation—for the sake of simplicity). Particularly:

FIG. 1 schematically shows a wafer at an intermediate stage of aproduction process of electronic devices to which the solution accordingto an embodiment may be applied;

FIG. 2 shows an enlarged portion of an electronic device implementing anindexing scheme known in the art, and

FIGS. 3A-3E show an enlarged portion of different examples of anelectronic device implementing an indexing scheme according to anembodiment.

DETAILED DESCRIPTION

With reference in particular to FIG. 1, there is schematically shown awafer 105 at an intermediate stage of a production process of electronicdevices, to which a solution according to an embodiment may be applied.The wafer 105 comprises of a circular slice (for example, with a radiusof 8 inches), which is mainly made of semiconductor material; anidentical electronic circuit 110 is integrated in a large number ofportions of the wafer 105 (for example, from some hundreds to somethousands). The production process of these integrated circuits 110 isexecuted in a sequence of stages, each one involving the patterning ofone or more exposed layers of the wafer 105 (for example, made ofsemiconductor, insulating, and/or conductive material) by means of acorresponding photolithographic mask. Particularly, in a productionprocess of the stepper shot type, at each stage of the productionprocess a mask being smaller than the wafer 105 is used to pattern acorresponding shot area 115 thereof, which only includes a subset of theintegrated circuits 110 that are patterned concurrently (with a singleshot) according to this mask. The wafer 105 is then moved so as toposition another shot area 115 thereof under the mask, and the sameoperations are repeated for the corresponding integrated circuits 110.The process is reiterated until the whole wafer 105 has been patterned.At the end of the production process, the portions of the wafer 105(wherein the desired integrated circuits 110 are formed) are cut bymeans of a sawing operation so as to obtain corresponding dice 120.

Each die 120 also includes (in addition to the corresponding integratedcircuit 110) an index 125, which is used to indicate a position of thedie 120 in the wafer 105 uniquely. Typically, the index 125 is formed inone of the last layers of the wafer 105, so as to be visible (directlyor indirectly) with a non-invasive inspection (for example, optically bymeans of a low power microscope). Particularly, when the above-describedproduction process of the stepper shot type is used, this (global) index125 has a composite structure with a shot index 125 s (which identifiesthe position of the corresponding shot area 115 in the wafer 105) and adie index 125 d (which identifies the position of the die 110 in thecorresponding shot area 115). The die index 125 d (being equal for allthe dice 110 in the same position within the different shot areas 115)may be formed during a selected stage of the production process by meansof a corresponding mask (which replicates the same die indexes 125 d inthe different shot areas 115). Conversely, the shot index 120 s(changing for the different shot areas 115) is formed by exploiting anadditional (service) mask, which creates one or more markers at the sameposition in all the corresponding dice 120. At every shot, the wafer 105is slightly displaced with respect to the service mask, so that themarkers move accordingly in the dice 120 of the corresponding shot area115; in this way, the position of the markers in each die 120 (withrespect to a predefined reference being formed thereon) allowsdistinguishing the different shot areas 115. These operations aretypically controlled by a software program that manages operation of astepper being used to create the electronic circuits 110 in the wafer105 (for example, being installed on a non-volatile memory of acorresponding control unit, for example, from a removable storagedevice, and loaded at least in part into its working memory when thiscontrol program is running).

Typically, the shot areas 115 are arranged in a matrix with Rs rows andCs columns (for example, Rs=Cs=6-12); therefore, each shot area 115 maybe identified in the corresponding shot index 125 s by a pair of row andcolumn coordinates. Likewise, the dice 120 are arranged in a matrix withRd rows and Cd columns (for example, Rd=Cd=10-100); therefore, each die120 may be identified in the corresponding die index 125 d by anotherpair of row and column coordinates. For example, the specific die 120being enlarged in the figure is identified by the shot index 125s=(2,3)—to indicate the shot area 115 in the 2nd row and the 3rd columnof the wafer 105—and by the die index 125 d=(4,5)—to indicate the die120 in the 4th row and the 5th column of this shot area 115.

An enlarged portion of an electronic device 200 implementing an indexingscheme is shown in FIG. 2. The electronic device 200 includes anintegrated circuit 210 that is formed in a die 220; the position of thedie 220 in the corresponding wafer (not shown in the figure) isindicated by a (global) index, which includes a (row shot) index 225Rsand a (column shot) index 225Cs—indicating the position of thecorresponding shot area in the wafer by means of its row and column,respectively—and a (row die) index 225Rd and a (column die) index225Cd—indicating the position of the die 210 in the corresponding shotarea by means of its row and column, respectively.

More in detail, each index 225Rs,225Cs,225Rd,225Cd includes a reference(for example, made of a reflective material such as metal); thisreference is formed by a ruler 230R with a comb-like structure for the(row) indexes 225Rs and 225Rd, and by another ruler 230C for the(column) indexes 225Cs and 225Cd—for example, being obtained bypatterning a metal layer of the die 220 with the mask being used at thecorresponding stage of its production process. The rulers 230R and 230Care arranged at a corner of the die 220; particularly, the rulers 230Rand 230C extend perpendicularly to each other (in parallel withcorresponding borders of the die 220) from an origin pad 235.

Each ruler 230R and 230C is used to measure a linear distance from theorigin pad 235 (along a straight line extending in parallel with thecorresponding border of the die 220). For this purpose, each ruler230R,230C is formed by an elongated spine 240R,240C and a plurality ofteeth 245R,245C, which project transversally from the spine 240R,240C(outwards); a portion of the spine 240R,240C between each pair ofadjacent teeth 245R,245C (or after a last tooth 245R,245C being distalfrom the reference pad 235) defines a corresponding inter-tooth250R,250C. A separation pad 255R,255C splits the (global) ruler230R,230C into a shot ruler 230Rs,230Cs for the (shot) index 225Rs,225Csand a die ruler 230Rd,230Cd for the (die) index 225Rd,225Cd;particularly, the ruler 230Rs,230Cs extends between the origin pad 235and the separation pad 255R,255C, while the ruler 230Rd,230Cd extendsfrom the separation pad 255R,255C away from the origin pad 235. Theteeth 245R,245C and the inter-teeth 250R,250C of each ruler 230Rs,230Rd, 230Cs, and 230Cd define an ordered alignment of locations thereof(referred to as dots), each one associated with a corresponding number;in the example shown in the figure, each ruler 230Rs,230Rd,230Cs,230Cdincludes 15 dots (numbered from 1 to 15)—moving upwards from the originpad 235 for the ruler 230Rs, upwards from the separation pad 255R forthe ruler 230Rd, leftwards from the origin pad 235 for the ruler 230Cs,and leftwards from the separation pad 255C for the ruler 230Cd.

A marker 260Rs, 260Rd, 260Cs, and 260Cd is used to select acorresponding dot (and then its number) in the ruler 230Rs, 230Rd,230Cs, and 230Cd, respectively. Each marker 260Rs,260Rd,260Cs,260Cd isdefined by the erasure of the corresponding dot—i.e., the missing of thecorresponding tooth 245R,245C or inter-tooth 250R,250C that exposes anopaque material (below the reflective material of the ruler230Rs,230Rd,230Cs,230Cd). The markers 260Rd and 260Cd for the (die)indexes 225Rd and 225Cd, respectively, may be formed by selectivelyremoving the metal layer of the corresponding rulers 230R and 230C withan additional mask (producing different markers 260Rd,260Cd in each die220 of the shot area, with the same markers 260Rd,260Cd that arerepeated in the same positions of the different shot areas); the markers260Rs and 260Cs for the (shot) indexes 225Rs and 225Cs, respectively,may likewise be formed by selectively removing the metal layer of thecorresponding rulers 230R and 230C with a suitable service mask that isslightly displaced at every shot (producing the same markers 260Rs,260Csin all the dice 220 of the shot area, with the markers 260Rs,260Cs thatchange in the different shot areas). For example, in the figure themarker 260Rs selects the dot 11 (for the index 225Rs) and the marker260Cs selects the dot 10 (for the index 225Cs)—so as to define the shotindex (11,10); moreover, the marker 260Rd selects the dot 2 (for theindex 225Rd) and the marker 260Cd selects the dot 4 (for the index225Cd)—so as to define the die index (2,4).

An enlarged portion of different examples of an electronic device 300implementing an indexing scheme according to an embodiment is shown inFIG. 3A-FIG. 3E. With reference in particular to FIG. 3A, the electronicdevice 300 includes an integrated circuit 310 that is formed in a die320; the position of the die 320 in the corresponding wafer (not shownin the figure) is indicated by a (global) index, which includes the samereference being formed by the rulers 230R and 230C. As above, the globalindex includes the (row shot) index 225Rs and the (column shot) index225Cs. However, the global index now includes a (row die) index 325Rdand a (column die) index 325Cd each one defined by multiple markers, forcorresponding digits that define a positional notation in a predefinedbase higher that 2.

In this way, it is possible to increase the maximum value of each index325Rd and 325Cd, and then the range of the whole index 325Rd,325Cd, forthe same size of the rulers 230Rd and 230Cd, respectively (or,vice-versa, it is possible to reduce the size of the rulers 230Rd and230Cd for the same maximum value of the indexes 325Rd and 325Cd). Theproposed solution thus allows indexing the dice 320 even when they areformed in large number in each shot area of the wafer (with a beneficialeffect on the quality management of the corresponding productionprocess).

It is emphasized that this result is achieved (by simply updating thecontrol program of the stepper) without the need of modifying the rulers230R and 230C. Therefore, the proposed solution only requires changingthe mask for the new markers (whereas it is possible to continue usingthe other masks, with a corresponding reduction of the implementationcost).

Particularly, in an embodiment of the invention each index 325Rd,325Cdis defined by a number in a decimal notation (i.e., with the base isequal to 10). Each number in base 10 is represented with an orderedsequence (from the right to the left) of the digits, which can take anyvalue from 0 to 10−1=9; the value of the number is then defined by thesum of its digit values, each one multiplied by a corresponding power ofthe base 10 (10.sup.0 for the first digit of the units, 10¹ for thesecond digit of the tens, 10² for the third digit of the hundreds, andso on). In the specific example at issue, the index 325Rd,325Cd includestwo digits (one for the units and another one of the tens).

In order to represent the different digits of the index 325Rd,325Cd, theruler 230Rd,230Cd is logically partitioned into a component330Rdu,330Cdu (referred to as units ruler) for the units digits, and acomponent 330Rdt,330Cdt (referred to as tens ruler) for the tens digits.The ruler 330Rdu,330Cdu includes 9 dots for all the possible non-nullvalue of the units digits from 1 to 9; the ruler 330Rdt,330Cdt includesthe remaining 6 dots for the first non-null values of the tens digitsfrom 1 to 6.

A marker 360Rdu, 360Rdt, 360Cdu, and 360Cdt is used as above to select acorresponding dot in the ruler 330Rdu, 330Rdt, 330Cdu, and 330Cdt,respectively; each marker 360Rdu,360Rdt,360Cdu,360Cdt then selects thecorresponding digit value 1-9, while the digit value 0 is represented bythe lacking of the marker 360Rdu,360Rdt,360Cdu,360Cdt in the ruler330Rdu,330Rdt,330Cdu,330Cdt. Particularly, the marker 360Rdu,360Cduselects the units digit of the index 325Rd,325Cd, while the marker360Rdt,360Cdt selects the tens digit of the index 325Rd,325Cd.Therefore, in the specific example at issue (wherein the tens digitvalue ranges from 0 to 6), the index 325Rd,325Cd can take any value from0 to 69. The proposed implementation thus increases the maximum value ofthe index 325Rd,325Cd (for the same ruler 230Rd,230Cd), with respect tothe above-described indexing techniques known in the art being based ona single marker, by (69−15)/16=360%. For example, in the figure themarker 360Rdu selects the dot of the units digit value 8, while themarker 360Rdt selects the dot of the tens digit 3—so as to define theindex 325Rd=38; likewise, the marker 360Cdu selects the dot of the unitsdigit value 3, while the marker 360Cdt selects the dot of the tens digitvalue 2—so as to define the index 325Cd=23.

A different value of the index 325Rd,325Cd of the same die 300 isillustrated in FIG. 3B. In this case, the marker for the ruler 330Rdu islacking to select the units digit value 0, while the marker 360Rdtselects the dot of the tens digit value 1—so as to define the index325Rd=10; the marker 360Cdu instead selects the dot of the units digitvalue 7, while the marker 360Cdt selects the dot of the tens digit value5—so as to define the index 325Cd=57.

Moving to FIG. 3C, the marker 360Rdu selects the dot of the units digitvalue 9, while the marker for the ruler 330Rdt is lacking to select thetens digit value 0—so as to define the index 325Rd=9; the marker 330Cduselects the dot of the units digit value 5, while the marker 360Cdtselects the dot of the tens digit value 3—so as to define the index325Cd=35.

With reference to FIG. 3D, the marker 360Rdu selects the dot of theunits digit value 7, while the marker for the ruler 330Rdt is lacking toselect the tens digit 0—so as to define the index 325Rd=7; the markerfor the ruler 330Cdu is lacking to select the units digit value 0, whilethe marker 360Cdt selects the dot of the tens digit value 1—so as todefine the index 325Cd=10. In this specific case (i.e., when both theindexes 325Rd and 325Cd are lower than or equal to 10) a single marker(i.e., for the units digits for values from 1 to 9, or for the tensdigits for the value 10) is present in each ruler 330Rd,330Cd;therefore, the indexing of the die 320 is exactly the same as in thedice known in the art.

At the end, in FIG. 3E the marker for the ruler 330Rdu is lacking toselect the units digit value 0, while the marker 360Rdt selects the dotof the tens digit value 6—so as to define the index 325Rd=60; the markerfor the ruler 330Cdu is likewise lacking to select the units digit value0, while the marker 360Cdt selects the dot of the tens digit value 3—soas to define the index 325Cd=30. In this specific case (i.e., when boththe indexes 325Rd and 325Cd are equal to a power of 10 being 2) a singlemarker for the tens digits is present in each ruler 330Rd,330Cd;therefore, the index 325Rd,325Cd has again exactly the same structure asin the dice known in the art, but it is now decoded in a different way.

As a further improvement, it is also possible to encrypt the index witha (secret) encryption key; in this way, the position of the die in thewafer can be recovered only by decrypting the index with the encryptionkey. This additional feature avoids making the position of the diepublic, so that this information is available only to authorized personsknowing the encryption key.

Particularly, in an embodiment the index is encrypted with a simplesubstitution algorithm, wherein each digit value of the index isreplaced with another digit value according to a (secret) substitutionalphabet—i.e., with each digit value Di (with i from 0 to the base ofthe positional notation minus 1) that is replaced with the i^(th) digitvalue in the substitution alphabet. For example, the substitutionalphabet 5942610387 indicates that the digit values 0, 1, 2, 3, 4, 5, 6,7, 8 and 9 are replaced by the digit values 5, 9, 2, 4, 6, 1, 0, 3, 8and 7, respectively:

-   -   0 1 2 3 4 5 6 7 8 9    -   5 9 4 2 6 1 0 3 8 7

Therefore, as an example, the index value 50 is encrypted to 15. Thesame operations described above are then repeated in reverse order torecover the actual value of the index from its encrypted version; forexample, a row die index equal to 32 and a column die index equal to 07indicates that the die is at the 73th row and at the 69th column in thecorresponding shot area.

Naturally, in order to satisfy local and specific requirements, a personskilled in the art may apply to the solution described above manylogical and/or physical modifications and alterations. Morespecifically, although this solution has been described with a certaindegree of particularity with reference to one or more embodimentsthereof, it should be understood that various omissions, substitutionsand changes in the form and details as well as other embodiments arepossible. Particularly, different embodiments of the invention may evenbe practiced without the specific details (such as the numericalexamples) set forth in the preceding description to provide a morethorough understanding thereof; conversely, well-known features may havebeen omitted or simplified in order not to obscure the description withunnecessary particulars. Moreover, it is expressly intended thatspecific elements and/or method steps described in connection with anyembodiment of the disclosed solution may be incorporated in any otherembodiment as a matter of general design choice.

For example, similar considerations apply if each electronic device hasa different structure or includes equivalent components (either separateto each other or combined together, in whole or in part); particularly,the electronic device may be of the micro-mechanical type, of theopto-electronic type, and the like; the electronic device may also be inthe form of a package (including one or more dice), or even in the formof a mere bare die.

Moreover, the wafer may be made of another material or it may include adifferent number of dice. Likewise, the indexes may be formed in anotherposition on the die or with other techniques (for example, with directwriting techniques by means of a laser); the indexes may also beinspected with alternative procedures (even when they are not opticallyvisible)—for example, by means of electromagnetic radiations (such asX-rays, infrared or ultraviolet light), or particle beams (such aselectron beams).

Even though in the preceding description reference has been made to twomarkers for each ruler, this is not to be interpreted in a limitativemanner (with the same concepts that also apply to three or moremarkers).

Similar considerations apply if the indexes have a different range (forexample, by providing a different number of dots for the tens digits, oreven by adding further dots for the hundred digits, and so on). The sametechnique may also be applied to indexes that are represented withnumbers in any other positional notation with any base higher than 2.

Consequently, the portion of the ruler dedicated to each marker mayinclude any number (>=2) of adjacent locations (down to 2 locations forthe digit values 1 and 2 when the base is equal to 3 and the digit value0 is represented by the lacking of the corresponding marker). Analternative implementation is also feasible wherein the markers havedifferent representations on a common ruler (for example, with themarker for the units digits and the marker for the tens digits that arearranged at opposite sides of the ruler).

Nothing prevents providing a specific dot for the digit 0 as well.Moreover, in a different implementation of the invention, 10 dots areused for the units digits (from 1 to 10); in this case, the values ofthe index up to 10 are represented only by the units marker, with thetens marker that is then used for higher values thereof.

The above-described implementation of the indexes based on the rulers ismerely illustrative, and it should not be interpreted in a limitativemanner; indeed, similar considerations apply if the indexes are simplydefined by the distance of the markers from a predefined reference(which may also comprise of an edge of the die).

More generally, the ruler may be implemented with any other structurecapable of measuring a linear distance from a corresponding originindicator, which ruler is provided with distance indicators in astraight linear arrangement from the origin indicator, each one defininga corresponding location of the ruler; for example, the ruler may beimplemented with the ruler may be implemented with a sequence of smallsegments each one representing a corresponding dot). Likewise, themarkers may be defined in any other way, for example, by deleting allthe dots up to the selected one, or by any other sign that is added tothe ruler (for example, in the form of a cross).

In addition or in alternative, the same technique may also be applied tothe shot index. In any case, the proposed solution lends itself to beused in standard production processes as well (wherein all the dice areformed concurrently in the whole wafer).

Similar considerations apply if each index has a different structure(for example, comprising of a single number that directly defines theposition of the die in the wafer).

Moreover, the indexes may be encrypted with any other algorithm (forexample, based on a shifted or reversed substitution, of thetransposition type, and the like); naturally, this feature is merelyoptional and in no way limitative.

It should be readily apparent that the proposed structure might be partof the design of the corresponding integrated circuits. The design mayalso be created in a programming language; moreover, if the designerdoes not fabricate dice or masks, the design may be transmitted byphysical means to others.

Moreover, the proposed electronic device may be mounted in intermediateproducts (such as mother boards), and/or coupled with one or more otherelectronic devices (such as a processor or a memory). In any case, theelectronic device is suitable to be used in complex systems (such asmobile telephones).

The proposed solution lends itself to be implemented with an equivalentmethod (by using similar steps, removing some steps being non-essential,or adding further optional steps); moreover, the steps may be performedin a different order, concurrently or in an interleaved way (at least inpart).

The above-described solution may be implemented as a stand-alone module,as a plug-in for the control program of the stepper, or even directly inthe control program itself. Moreover, the control program may take anyform suitable to be used by the control unit of the stepper (or by anyother data processing system) or in connection therewith. In any case,the solution according to an embodiment of the present invention lendsitself to be implemented even with a hardware structure (for example,integrated in a chip of semiconductor material), or with a combinationof software and hardware.

Such alterations, modifications, and improvements are intended to bepart of this disclosure, and are intended to be within the spirit andthe scope of the present invention. Accordingly, the foregoingdescription is by way of example only and is not intended to belimiting. The present invention is limited only as defined in thefollowing claims and the equivalents thereto.

The invention claimed is:
 1. An electronic device, comprising: a diehaving a positional location in a shot defined by first and second diecoordinates, wherein the shot has a positional location in a waferdefined by first and second shot coordinates, wherein the first diecoordinate identifies a horizontal location in the shot where the diewas formed, wherein the second die coordinate identifies a verticallocation in the shot where the die was formed, wherein the first shotcoordinate identifies a horizontal location on the wafer where the shotresides, wherein the second shot coordinate identifies a verticallocation on the wafer where the shot resides; a first comb structurecomprising a first spine with a first plurality of teeth projectingtransversally therefrom, and wherein portions of the first spine betweenpairs of adjacent teeth of the first plurality of teeth define firstinter-tooth portions, the first plurality of teeth and first inter-toothportions defining a first contiguous arrangement of first dots, a secondcomb structure comprising a second spine with a second plurality ofteeth projecting transversally therefrom, and wherein portions of thesecond spine between pairs of adjacent teeth of the second plurality ofteeth define second inter-tooth portions, the second plurality of teethand second inter-tooth portions defining a second contiguous arrangementof second dots, a first marker at a selected one of the first dots, thefirst marker indicating a first digit of a two digit number for thefirst die coordinate, a first additional marker at a selected one of thefirst dots, the first additional marker indicating a second digit of thetwo digit number for the first die coordinate, a second marker at aselected one of the second dots, the second marker indicating a firstdigit of a two digit number for the second die coordinate, and a secondadditional marker at a selected one of the second dots, the secondadditional marker indicating a second digit of the two digit number forthe second die coordinate.
 2. The electronic device of claim 1, whereinfirst dots and the second dots are arranged in a linear configuration.3. The electronic device of claim 1, wherein the first digit of thefirst die coordinate has a units weight for the two digit number and thesecond digit of the first die coordinate has a tens weight for the twodigit number; and wherein the first digit of the second die coordinatehas a units weight for the two digit number and the second digit of thesecond die coordinate has a tens weight for the two digit number.
 4. Theelectronic device of claim 3, wherein a lack of the first marker orfirst additional marker indicates a null or zero value of the first orsecond digit of the first die coordinate, respectively; and wherein alack of the second marker or second additional marker indicates a nullor zero value of the first or second digit of the second die coordinate,respectively.
 5. The electronic device of claim 1, wherein the firstand/or second comb structure includes an origin pad.
 6. The electronicdevice of claim 1, wherein the first marker indicates an encrypted firstdigit of the first die coordinate and wherein the first additionalmarker indicates an encrypted second digit of the first die coordinate;and wherein the second marker indicates an encrypted first digit of thesecond die coordinate and wherein the second additional marker indicatesan encrypted second digit of the second die coordinate.
 7. Theelectronic device of claim 1, further comprising: a third comb structurecomprising a third spine with a third plurality of teeth projectingtransversally therefrom, and wherein portions of the third spine betweenpairs of adjacent teeth of the third plurality of teeth define thirdinter-tooth portions, the third plurality of teeth and the thirdinter-tooth portions defining a third contiguous arrangement of thirddots, a first separation pad connecting the first and third spines; afourth comb structure comprising a fourth spine with a fourth pluralityof teeth projecting transversally therefrom, and wherein portions of thethird spine between pairs of adjacent teeth of the fourth plurality ofteeth define fourth inter-tooth portions, the fourth plurality of teethand the fourth inter-tooth portions defining a fourth contiguousarrangement of fourth dots; a second separation pad connecting thesecond and fourth spines; a third marker at a selected one of the thirddots, the third marker indicating a digit number of the first shotcoordinate; and a fourth marker at a selected one of the fourth dots,the fourth marker indicating a digit number of the second shotcoordinate.
 8. A method, comprising: forming dice in a wafer, with eachdie having a positional location in a shot defined by first and seconddie coordinates, wherein each shot has a positional location in thewafer defined by first and second shot coordinates, wherein the firstdie coordinate identifies a horizontal location of the die in the shot,wherein the second die coordinate identifies a vertical location of thedie in the shot, wherein the first shot coordinate identifies ahorizontal location on the wafer where the shot resides, wherein thesecond shot coordinate identifies a vertical location on the wafer wherethe shot resides; and forming a first comb structure on each die andcomprising a first spine with a first plurality of teeth projectingtransversally therefrom, and wherein portions of the first spine betweenpairs of adjacent teeth of the first plurality of teeth define firstinter-tooth portions, the first plurality of teeth and first inter-toothportions defining a first contiguous arrangement of first dots at eachdie location on the wafer, forming a second comb structure on each dieand comprising a second spine with a second plurality of teethprojecting transversally therefrom, and wherein portions of the secondspine between pairs of adjacent teeth of the second plurality of teethdefine second inter-tooth portions, the second plurality of teeth andsecond inter-tooth portions defining a second contiguous arrangement ofsecond dots on the wafer, placing a first marker at a selected one ofthe first dots, the first marker indicating a first digit of a two digitnumber for the first die coordinate, placing a first additional markerat a selected one of the first dots, the first additional markerindicating a second digit of the two digit number for the first diecoordinate, placing a second marker at a selected one of the seconddots, the second marker indicating a first digit of a two digit numberfor the second die coordinate, and placing a second additional marker ata selected one of the second dots, the second additional markerindicating a second digit of the two digit number for the second diecoordinate.
 9. The method of claim 8, wherein first dots and the seconddots are arranged in a linear configuration.
 10. The method of claim 9,wherein the first digit of the first die coordinate has a units weightfor the two digit number and the second digit of the first diecoordinate has a tens weight for the two digit number; and wherein thefirst digit of the second die coordinate has a units weight for the twodigit number and the second digit of the second die coordinate has atens weight for the two digit number.
 11. The method of claim 10,wherein a lack of the first marker or first additional marker indicatesa null or zero value of the first or second digit of the first diecoordinate, respectively; and wherein a lack of the second marker orsecond additional marker indicates a null or zero value of the first orsecond digit of the second die coordinate, respectively.
 12. The methodof claim 9, wherein the first and second comb structure each include anorigin pad; wherein a value of the first die coordinate is based on adistance of the first marker and first additional marker from the originpad of the first comb structure; and wherein the value of the second diecoordinate and second shot coordinate is based on a distance of thesecond marker and second additional marker from the origin pad of thesecond comb structure.
 13. A method for indexing electronic devices,comprising the steps of: integrating a plurality of electronic circuitsinto portions of a wafer for corresponding dice, each die having aspecific die location in the wafer; forming at least one index on eachdie, each index including a reference defining an ordered alignment of aplurality of locations on the die and marker means for defining a valueof the die location according to an arrangement of the marker means withrespect to the reference, the value of the index indicating the specificdie location of the die in the wafer; and cutting the dice for formingelectronic devices; wherein the step of forming at least one indexincludes, for each index, forming a plurality of markers each onearranged at a selected one of the locations, the selected location ofthe marker defining a value of a digit associated with a correspondingpower of a base higher than 2 within a number in a positional notationin said base representing the value of the index.
 14. The methodaccording to claim 13, wherein the ordered alignment of the locations islogically partitioned into a plurality of location subsets each onecomprising of a plurality of consecutive locations for a correspondingmarker, the step of forming at least one index on each die includingforming each marker in a location of a corresponding location subset.15. The method according to claim 13, wherein the step of forming atleast one index on each die includes not forming a corresponding markerfor defining a null value of each digit.
 16. The method according toclaim 13, wherein the step of forming at least one index on each dieincludes: forming a reference of each index to include an originindicator and a plurality of distance indicators extending along astraight line from the origin indicator, each distance indicatordefining a corresponding location of the reference.
 17. The methodaccording to claim 16, wherein the step of forming a reference of eachindex includes: forming the reference to include a comb-like structurehaving a spine and a plurality of teeth projecting from the spine, eachportion of the spine between a pair of adjacent teeth defining acorresponding inter-tooth, each tooth and each inter-tooth identifying acorresponding location of the reference, and wherein the step of forminga plurality of markers includes forming each marker to include of eithera missing tooth or a missing inter-tooth.
 18. The method according toclaim 13, wherein the step of integrating a plurality of electroniccircuits includes: making a die subset comprising of a predeterminednumber of the dice concurrently in each one of a plurality of shot areasof the wafer, the die subsets being made in succession in the wafer, andwherein the step of forming at least one index on each die includessetting the value of the at least one index to indicate a die locationof the die in the corresponding shot area.
 19. The method according toclaim 18, wherein the step of making a die subset includes: arrangingthe dice of the die subset in a matrix having a plurality of rows and aplurality of columns; and wherein the step of forming at least oneindex) on each die includes: forming a row index and a column index, therow index being indicative of the row of the die in the matrix and thecolumn index being indicative of the column of the die in the matrix.20. The method according to claim 13, wherein the step of forming atleast one index on each die includes encrypting a value of each indexwith an encryption key.
 21. An electronic device, comprising: a diehaving a positional location within a shot defined by first and secondtwo digit die coordinate values, wherein the first two digit diecoordinate value identifies a horizontal location within the shot wherethe die was formed, and wherein the second two digit die coordinatevalue identifies a vertical location within the shot where the die wasformed; and an index formed on the die, the index comprising: a firstcomb structure comprising a first contiguous arrangement of first dots,a second comb structure comprising a second contiguous arrangement ofsecond dots, a first marker at a first selected one of the first dots,the first marker specifying a first digit of the first two digit diecoordinate value, a second marker at a second selected one of the firstdots, the second marker specifying a second digit of the first two digitdie coordinate value, a third marker at a first selected one of thesecond dots, the third marker specifying a first digit of the second twodigit die coordinate value, and a fourth marker at a second selected oneof the second dots, the fourth marker specifying a second digit of thesecond two digit die coordinate value.
 22. The electronic device ofclaim 21, wherein the first dots are located at teeth or spaces betweenteeth in the first comb structure; and wherein the second dots arelocated at teeth or spaces between teeth in the second comb structure.23. The electronic device of claim 21, wherein each first digitspecifies a units weight for the two digit die coordinate value and eachsecond digit specifies a tens weight for the two digit die coordinatevalue.
 24. The electronic device of claim 21, wherein absence of one ofthe first through fourth markers indicates a null value of thecorresponding first or second digit.